A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs) or other functional devices. In such a case, a patterning device (e.g., a mask) may contain or provide a pattern corresponding to an individual layer of the device (“design layout”), and this pattern can be transferred onto a target portion (e.g., including one or more dies) on a substrate (e.g., silicon wafer) that has been coated with a layer of radiation-sensitive material (“resist”), by methods such as irradiating the target portion through the pattern on the patterning device. In general, a single substrate contains a plurality of adjacent target portions to which the pattern is transferred successively by the lithographic apparatus, one target portion at a time. In one type of lithographic apparatus, the pattern on the entire patterning device is transferred onto one target portion in one go; such an apparatus is commonly referred to as a wafer stepper. In an alternative apparatus, commonly referred to as a step-and-scan apparatus, a projection beam scans over the patterning device in a given reference direction (the “scanning” direction) while synchronously moving the substrate parallel or anti-parallel to this reference direction. Different portions of the pattern on the patterning device are transferred to one target portion progressively.
Prior to transferring the pattern from the patterning device to the substrate, the substrate may undergo various procedures, such as priming, resist coating and a soft bake. After exposure, the substrate may be subjected to other procedures, such as a post-exposure bake (PEB), development, a hard bake and measurement/inspection of the transferred pattern. This array of procedures is used as a basis to make an individual layer of a device, e.g., an IC. The substrate may then undergo various procedures such as etching, ion-implantation (doping), metallization, oxidation, chemo-mechanical polishing, etc., all intended to finish off the individual layer of the device. If several layers are used in the device, then some or all of these procedures or a variant thereof may be repeated for each layer. Eventually, a device will be present in each target portion on the substrate. If there is a plurality of devices, these devices are then separated from one another by a technique such as dicing or sawing, whence the individual devices can be mounted on a carrier, connected to pins, etc.
Thus, manufacturing devices, such as semiconductor devices, typically involves processing a substrate (e.g., a semiconductor wafer) using a number of fabrication processes to form various features and multiple layers of the devices. Such layers and features are typically manufactured and processed using, e.g., deposition, lithography, etch, chemical-mechanical polishing, and ion implantation. Multiple devices may be fabricated on a plurality of dies on a substrate and then separated into individual devices. This device manufacturing process may be considered a patterning process. A patterning process involves a patterning step, such as optical and/or nanoimprint lithography using a patterning device in a lithographic apparatus, to transfer a pattern on the patterning device to a substrate and typically, but optionally, involves one or more related pattern processing steps, such as resist development by a development apparatus, baking of the substrate using a bake tool, etching using the pattern using an etch apparatus, etc.
For example, US 2004/0227915 A1 relates generally to an optical system and an exposure apparatus having the same. More particularly, the disclosure of US 2004/0227915 A1 is applicable to an optical system to be used in a photolithographic process wherein light of very short wavelength, called extreme ultraviolet (EUV) light, is used to project a pattern of a reticle onto a wafer, for manufacture of semiconductor devices such as ICs. In order to produce a high-precision optical system, the optical elements within such an apparatus are desirably positioned and oriented very exactly, which is why the optical elements are typically measured relatively to a defined reference before or even during operation. Therefore, complex measurement systems need to be integrated into the lithographic apparatus which are typically mounted on one or more metrology (sensor) frame structures. It is known to arrange the parts of the measurement system, e.g., the individual sensors, around the optical elements to be measured. However, a drawback of the known solutions is the relatively huge dimension of such lithographic apparatuses, resulting from the surrounding metrology frame structure. Furthermore, the known frames are susceptible to vibrations and the commonly used multi-part designs of the metrology frame usually leads to increased measurement inaccuracy, as the positions of the several parts of the frame and thus the sensors which are mounted on the different parts of the frame relative to each other may be misaligned or rather prone to component tolerances.